1. Field of the Invention
This invention relates to a dust-free, vented product pump arrangement including apparatus for receiving particulate matter from a container by which the matter was transported and filtering from the ambient atmosphere dust particles produced by transfer of the particulate matter to the receiving apparatus and pump system for moving the product from the discharge of the product receiver to one or more collecting points, said system including a dense-phase, positive-pressure, pneumatic conveying pump. The invention more particularly relates to dust-free pump arrangements which may be used to discharge dry, free-flowing particulate materials into pressurized vessels or into liquids that have a high system back pressure. The invention also relates to pump assemblies which can be used to convey products that are normally dusty, light and fluffy or otherwise have poor flow and handling characteristics.
2. Description of the Prior Art
Small quick cycling product pumps have frequently been used as a means of introducing product into a pneumatic conveying line. Each successive cycle of such pump pushed a new charge of product into the conveying line and the gas trapped between each charge pushed the previously-loaded charge further along the conveying line. These devices were normally cycled with electric or pneumatic controls incorporating adjustable timing devices. The timers were arranged to vary the time of each function within the cycle so that the system could be adjusted to meet varying field conditions. The cycle started with the product inlet valve open and the product flowed by gravity from the hopper, or the like, into the product pump. After a short fill time, the product inlet valve was closed and pressure was applied to the pump chamber to pneumatically force the product charge from the pump into the conveying line. After the pressure source was shut off, pressure remained in the product pump and in the conveying line. Some of this pressure was dissipated through the product charge opening and through the discharge of the conveying system providing a sufficient delay time was employed between the shut off of the pressure source and the opening of the product inlet valve. In actual practice, a delay time was selected to permit some pressure to bleed off through the discharge lines with the remaining pressure discharging into the incoming product when the inlet valve was opened. Both the time required to bleed off the pressure and the blow back through the inlet caused a reduction in the overall delivery rate of the pneumatic conveying system. Manifestly, the higher the back pressure at the discharge of the system the greater the bleed off problem. Also, a high rate of blow back at the inlet feed point often caused a dust problem. It is further noted that the prior art systems often could not be used to transport solids to a highly pressurized vessel or into a liquid where there was a large hydraulic back pressure.
Another ever increasing problem in today's industrial environment has occurred in the handling of particulate materials which are capable of producing airborne dust. This problem is particularly acute when it is necessary to transfer dusty materials from, for example, a transport container, to processing machinery. The dust produced during this operation is well known to constitute a hazard to human health, as well as in some circumstances creating other risks such as producing an explosive atmosphere. Due to these risks, numerous laws have been enacted to require industries handling such materials to remove significant portions of this dust from the air, and the stringent nature of these laws have created the need for effective and efficient filtering mechanisms.
From an economic viewpoint, these filtering mechanisms also assume importance in that the airborne dust is a recoverable portion of the particulate material in question. Accordingly, in addition to the significance of environmental and legal requirements for dust recovery, recovery of dust particles assumes importance in the prevention of economic loss arising out of loss of raw materials in the form of dust particles.